| Category: Lighting , Specifications | Audience: General
The following research reports and papers have been complied over time to address identified gaps in international and New Zealand road safety and lighting research. The research findings have been used to refine Waka Kotahi road safety and lighting guidance and specifications and to inform the joint Australia/New Zealand road and public lighting standard - AS/NZS 1158 series.
Related information:
This project aimed to improve understanding of how the quantity and quality of road lighting influences the frequency of night-time crashes in urban areas with speed limits less than 80km/h. While it is well-established that improving lighting increases safety, no well-established dose response relationship to lighting parameters exists from which one can deduce benchmark levels of lighting for safety.
This study looked at a sample of street lighting installations spread over the urban areas of nine territorial local authorities. Standard street lighting parameters were measured in the field using a variety of instruments including illuminance meter, luminance meter and a calibrated digital camera. Field measurements were related to the ratio of night-time to day-time crashes (from the CAS database) as a measure of night-time safety vis-à-vis daytime safety.
How does the level of road lighting affect crashes in New Zealand – A pilot study [PDF, 1.7 MB]
CloseAdaptive lighting is appropriate where the lighting is to be varied at different times according to a weighting, for example off-peak, during better weather or worse weather, at the weekend, when there are more vulnerable road users around or when there is more ambient light. Here a higher or lower level of lighting can be selected from the range of subcategories available.
Generally, only the luminance will be varied as uniformity is consistent across all levels of category V lighting. Recent urban research benchmarks the level of lighting to specific road safety outcomes. With the benefit of this benchmarking, it is possible to better assess the impact of changes in road lighting on road safety and assess these changes against Safe System criteria. This review looks at the safety of adaptive lighting generically, rather than from the viewpoint of any one technology. However, the technology is most suited to LED Luminaires and due to concerns about energy use and carbon emissions, there is likely to be significant dimming associated with adaptive lighting.
The impact of adaptive road lighting on road safety: A literature review [PDF, 890 KB]
CloseIt is known that road lighting has significant safety benefits. Before and after studies both in New Zealand and overseas indicate reductions in crashes of around 30% where lighting has been improved. This project aimed to improve our understanding of how the quality of road lighting influenced the number of night-time crashes on higher-speed roads generally on the urban fringe. It complements previous 2012 urban-based work by extending it to higher-speed (80 and 100km/h) roads in an urban fringe context, where the traffic conditions and types of crash are very different from urban areas and where it was expected that the relationships between lighting parameters and crash experience would also be different.
Closep>Recent work has shown that the safety of urban roads at night varies with the amount of lighting. This enables us to look at the benefits and costs of providing different levels of lighting and using different light sources. The highest benefit cost ratios are achieved at the highest traffic volumes and when the pavement is most highly lit. Results indicate that best levels for safety are in the higher light levels (Cat V2 and above) and that the benefits of road lighting often substantially exceed the costs, including the energy costs. Adaptive LED lighting offers lower crash benefits and reduced energy consumption. In the interests of providing a safe road network, at current costs higher lighting levels are worthy of serious consideration. Also, the proposed changes to the NZ R-Table in the current lighting standard (now published as AS/NZS 1158 Part 1.1 (2020) do not markedly increase costs—if anything costs could reduce if the specular NZN4 R-Table is no longer used. Therefore, no economic case exists for RCAs to choose a lower lighting subcategory.
The benefits and costs associated with urban road lighting in NZ(external link)
CloseThis technical note reviews issues related to the dark/light and light/dark eye adaptations necessary when a driver passes between lit and unlit road sections. It considers minimum unlit distances for road lengths prescribed by some international jurisdictions and reports on the results of a crash study of sections of State Highway 1 and State Highway 2 near Wellington, New Zealand where lit sections are interspersed with unlit sections.
The technical note makes a recommendation regarding the minimum length for unlit sections on New Zealand roads where the unlit sections are abutted at each end by lit sections.
Road lighting - A review of minimum unlit distance between lit sections [PDF, 1.2 MB]
CloseThis report reviewed evidence from laboratory trials and some specifically set up on-road scenarios to consider the concept that visibility is improved by the wider spectrum achieved by “white” light sources of road lighting like LEDs. This effect is much more pronounced at category P lighting levels than at category V lighting levels. The relationship between road safety and the colour of light is multifactorial and no on-road studies been carried out to establish a direct linkage between the colour of light and crashes. The colour rendition characteristics of both white light and warm white light as emitted by LEDs exceed by a wide margin that of HPS (LED CRI> 70%, HPS CRI ~24%). The report concludes that there is no evidence of any safety difference between white LED lighting and “warm white” LED lighting.
CloseThis project aims to improve our understanding of how flag lighting (ie one to three lights at rural intersections) influences the number of night-time crashes. It is known that road lighting has significant safety benefits. Before and after studies both here and overseas indicate reductions in crashes of around 30% where route lighting has been improved. There is persuasive evidence from overseas that flag lighting is a legitimate and useful road safety tool but to date local information has been lacking. The project used a database of state highway intersection crashes and intersection characteristics produced by the use of the CAS system of Police reported crashes matched to a number of databases containing road infrastructure and vehicle flow information.
CloseThis report looks at the advantages and disadvantages of lights with more or less blue in their spectra. This is because the main difference between HPS light and LED is the lower proportion of blue light in HPS compared to LED. Blue light comes with advantages and disadvantages, and little has been done to properly weight the advantages and disadvantages.
In general, with LED technology, in the colour temperature range up to around 4000K, the higher the colour temperature the higher the lumens per watt or efficacy, so all things being equal a 4000K light will be preferred by a designer to a 3000k light. However, the efficacies of LED luminaires in that range are expected to converge between 2020 and 2025 removing that efficacy advantage.
The review covers issues related to:
Sky glow modelling has demonstrated that light emitted above the horizontal from a light source is often a critical factor in determining the total sky glow from that light source. To quantify the extent and magnitude of upward light five high Wellington vantage points were chosen as observation sites. Measurements were made of the direct light from visible floodlights, streetlights and illuminated signs using multiple exposures with a calibrated DSLR camera.
Floodlights were the strongest single source of upward light producing between 10 and 150 times more upward light than a single 150 watt HPS road light. The average value was 50 times more upward light.
HPS road lighting luminaires produced an average of 130 candelas of upward light, but no measurable upward light was detected from LED road lighting luminaires.
CloseGlobally light from artificial sources has been growing at a rate greater than the global population growth. Technological changes have allowed light to be produced at a lower net cost and the recent advent of LED technology has delivered light sources capable of delivering broad spectrum light with an enriched blue content. Light at the blue end of the spectrum scatters more readily in the atmosphere and has raised concerns that the enriched blue content in itself is accelerating the loss of a dark night sky.
Authorities in New Zealand have attempted to address the issue by choosing a lower correlated colour temperature (CCT) for their luminaires. For example, 4000K (Waka Kotahi NZ Transport Agency) or 3000K (eg Dunedin City). However, the CCT is not an intrinsic measure of sky glow potential, rather it is a measure of the colour or “warmth” of a light source. A lower value for the CCT may indicate less sky glow but this is not always the case. At the extreme it is possible for a luminaire spectrum rated at 3000K to produce more sky glow than one rated at 4000K.
This report considers alternative means to assess risk of sky glow contribution using data gather using a handheld spectrometer to record the spectral power distribution (SPD) of the luminaire at the point of measurement between the wavelengths 380nm to 780nm - the extent of visible light. Using the recorded SPD data, five common spectral indexes of luminaire light output were calculated using the US Department of Energy (DOE) “Sky Glow Comparison Tool” methodology and examined for their ability to predict the resulting sky glow.
The spectral indexes were:
Streetlighting related sky glow is a legitimate concern but local information about its prevalence and importance is sparse. This project was a first step towards providing such information. Part 1 investigated spatial aspects of sky glow in two relatively dark rural highway settings and part 2 investigated the temporal aspects of sky glow in the Wellington CBD to identify contributions from a range of artificial light sources. A calibrated DSLR camera was used to estimate sky glow.
Part 1 used a series of sky glow measurements up to 2km along roads aligned at right angles to SH1 lighting at Peka Peka (LED) and MacKays Crossing (HPS). At both sites the sky glow decayed asymptotically reaching minima 1.5 to 2 km from the highway. At Peka Peka the maximum contribution to sky glow from the SH1 lighting was estimated at 0.097 mcd/m2 and at MacKays Crossing 0.18 mcd/m2, somewhat higher than that at Peka Peka.
Part 2 investigated the relative contributions to sky glow from various artificial light sources throughout the night. These included variable light from high rise buildings, houses and flats, vehicle headlights and static (unvarying) lights from streetlights, port lighting, railyard lighting, security lighting, and advertising signs. Data sources on these temporal changes were two sets of all-night time-lapse photographs taken from the roof of the Met Service building in Wellington and council traffic volume data, which relates to headlight usage. Static lighting was the most important contributor, followed by high rise and residential buildings, which had dissimilar temporal patterns. Car headlights made a relatively small contribution. The ranges found were:
The relative contributions from each static source could not be isolated and await further research.
Road lighting - Its night sky impact [PDF, 1021 KB]
CloseIn September 2011 a rural, 100km/h, approximately 7 km section of State highway 22 was lit to V3 standard using LED luminaires. This was the first category V installation installed in New Zealand which used LED lighting. Previously there was no route lighting in place, just some intersection flag lights. The LED installation has centrally controlled dimming capability and was dimmed after midnight to a level of V4/V5.
The purpose of this study was to discover any evidence of a positive safety impact associated with the lighting and any impact of the post-midnight dimming.
Analyses were carried out for the following before and after periods:
The comparisons were carried out for all types of crash movements and also after excluding crash movements C and D which are single vehicle crashes involving loss of control, leaving the road and cornering. These C and D types of crashes tend not to be influenced downwards by lighting so may obscure positive changes in other movement categories. C and D movement crashes are also considered separately. as there is a possibility that lighting may sometimes be associated with increases in these crashes, possibly by way of improving the driver perceived road environment enough for some drivers to choose imprudently higher speeds. Only crashes involving injury were included in the analyses.
The conclusions made were that:
The safety impact of lighting on a previously unlit section of SH22 [PDF, 462 KB]
CloseRoute streetlighting’s main objective is to allow drivers to see obstacles on the road. A secondary objective is to allow them to see objects on the roadside (such as pedestrians and vehicles on driveways) which have the potential to become obstacles on the road. If not carefully controlled streetlighting also can generate unintended consequences. It is also a duty of lighting designers to provide the required lighting as efficiently as possible in terms of electricity usage, This has led road controlling authorities to replace High Pressure Sodium (HPS) lamps with Light Emitting Diode (LED) luminaires which use far less energy and can be more easily controlled.
LEDs tend to have a greater proportion of their spectra in the lower wavelength blue region than HPS lamps and there is considerable spectral variation between various LEDs. It is not yet clear what impact (if any) this spectral shift has on road safety or its other impacts.
This report looks at how the shift from HPS may impact on safety and other possible unintended consequences of the change. A table of pros and cons has been produced detailing identified aspects for consideration. The identified safety negatives are all ameliorated by reducing the amount of blue light. The safety positives all involve greater blue light. However, the evidence for the positives is weaker than that of the negatives. At the worst the amelioration, by bringing the SPDs of LEDs in line with that of HPS is unlikely to make the safety impact of LEDs any worse than HPS.
It was concluded that on the balance of probabilities there are safety benefits in reducing the proportion of blue wavelengths in route lighting. Bringing the SPDs of LEDs in line with those typical of HPS is unlikely to make the safety impact of LEDs less than that of HPS. There are also environmental benefits.
The Road Safety and Environmental Impact of LED Spectra in route lighting [PDF, 1.2 MB]
CloseThis report reviews the impact of streetlighting on human sleep patterns. The human body has a 24 hour circadian rhythm, the characteristics of which are largely determined by the light environment. The light which controls the circadian rhythm also powerfully impacts the body’s endocrine system which results in behavioural impacts and health impacts when the normal functioning of the endocrine system is disturbed. .. One of these impacts can be sleep disturbance.
Melatonin is a hormone produced by the body and is intimately related to circadian rhythms. These rhythms impact the levels of melatonin in the blood and saliva.. Saliva or plasma Melatonin levels compared with the normal range of melatonin levels at different times of the day are often used a s a surrogate for sleep and circadian rhythm disturbance.
An important determinant of the circadian rhythm is light stimulation of the cells of the retina. It is known that bluer light preferentially stimulates these cells so excessive blue light is an important causative factor in these disturbances.. Too much lighting at night can suppress melatonin production which may indicate disturbed sleep patterns. and circadian rhythms. The amount of light necessary to disturb the daily melatonin rhythm is considerably higher than that required to merely change melatonin levels.
This review looks at three sources of information:
Conclusions are then made regarding the likely impact of LED streetlighting on human sleep based on circadian impact metrics and night melatonin levels as a surrogate for the impact of the lighting on sleep...
A concise review of the impact of LED streetlighting on human sleep [PDF, 939 KB]
Close